Compressor flowpath

ABSTRACT

A core flowpath through a low pressure compressor section of a gas turbine engine includes an outer diameter, which has a slope angle relative to an axis defined by the core flowpath. The slope angle is a slope angle that is operable to prevent flow separation of a fluid passing through the core flowpath.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to U.S. Provisional ApplicationNo. 61/593001, which was filed on Jan. 31, 2012, and is incorporatedherein by reference.

TECHNICAL FIELD

The present application relates generally to gas turbine engines, andmore particularly to a low pressure compressor flowpath for a gasturbine engine.

BACKGROUND OF THE INVENTION

Commercial turbofan engines use low pressure compressors coupled to afan. Advances in coupling the fan to the low pressure compressor haveallowed the compressor to operate at higher speeds and to decrease thenumber of compressor stages required of the compressor. Decreasing thenumber of stages and increasing the rotational speed of the low pressurecompressor causes existing flowpath designs to be non-optimal andresults in decreased performance when the existing flowpath designs areused.

SUMMARY OF THE INVENTION

A turbine engine according to an exemplary aspect of the presentdisclosure includes, among other things, a compressor section having atleast a low pressure compressor, and a core flowpath passing through thelow pressure compressor, the core flowpath having an inner diameter andan outer diameter. The outer diameter has a slope angle of betweenapproximately 0 degrees and approximately 15 degrees relative to anengine central longitudinal axis. The turbine engine may also include acombustor in fluid communication with the compressor section, and aturbine section in fluid communication with the combustor.

In a further non-limiting embodiment of the foregoing turbine engine,the turbine engine may include a fan.

In a further non-limiting embodiment of either of the foregoing turbineengines, the turbine engine may include a fan connected to at least alow speed spool through a geared architecture.

In a further non-limiting embodiment of any of the foregoing turbineengines, the turbine engine may include a slope angle in the range ofapproximately 0 degrees to approximately 10 degrees relative to theengine central longitudinal axis.

In a further non-limiting embodiment of any of the foregoing turbineengines, the turbine engine may include a slope angle that isapproximately 6 degrees relative to the engine central longitudinalaxis.

In a further non-limiting embodiment of any of the foregoing turbineengines, the turbine engine may include a slope angle in the range ofapproximately 5 degrees to 7 degrees, relative to the engine centrallongitudinal axis.

In a further non-limiting embodiment of any of the foregoing turbineengines, the turbine engine may include a slope angle that slopes towardthe engine central longitudinal axis along a fluid flow direction of thecore flowpath.

In a further non-limiting embodiment of any of the foregoing turbineengines, the turbine engine may include a low pressure compressor thatcomprises at least one variable vane.

In a further non-limiting embodiment of any of the foregoing turbineengines, the turbine engine may include a low pressure compressorfurther comprising an exit guide vane, wherein the exit guide vane islocated in a low pressure compressor outlet section of the coreflowpath.

In a further non-limiting embodiment of any of the foregoing turbineengines, the turbine engine may include a low pressure compressorfurther comprising a low pressure bleed located between a low pressurecompressor rotor and the exit guide vane.

In a further non-limiting embodiment of any of the foregoing turbineengines, the turbine engine may include a low pressure bleed furthercomprising a bleed trailing edge. The bleed trailing edge may extendinto the core flowpath beyond the outer diameter of the core flowpath.

In a further non-limiting embodiment of any of the foregoing turbineengines, the turbine engine may include a low pressure compressor thatis a multi-stage compressor.

In a further non-limiting embodiment of any of the foregoing turbineengines, the turbine engine may include an inner diameter of the coreflowpath that increases through the low pressure compressor along afluid flow direction.

In a further non-limiting embodiment of any of the foregoing turbineengines, the turbine engine may include an outer diameter slope anglethat is operable to reduce a tip clearance of a compressor rotor, andthereby reduce flow separation.

A low pressure compressor for a turbine engine according to an exemplaryaspect of the present disclosure includes, among other things, a coreflowpath, wherein the core flowpath has an inner diameter and an outerdiameter. The outer diameter has a slope angle of between approximately0 degrees and approximately 15 degrees relative to an engine centrallongitudinal axis about which the low pressure compressor rotates.

In a further non-limiting embodiment of the foregoing low pressurecompressor, the low pressure compressor may include a slope angle thatis between approximately 0 degrees and approximately 10 degrees.

In a further non-limiting embodiment of either of the foregoing lowpressure compressor, the low pressure compressor may include a slopeangle that is approximately 6 degrees.

In a further non-limiting embodiment of any of the foregoing lowpressure compressor, the low pressure compressor may include at leastone variable vane.

In a further non-limiting embodiment of any of the foregoing lowpressure compressor, the low pressure compressor may include an outletsection of the core flowpath. The outlet section may include an exitguide vane.

In a further non-limiting embodiment of any of the foregoing lowpressure compressor, the low pressure compressor may include a lowpressure bleed located between a low pressure compressor rotor and theexit guide vane.

In a further non-limiting embodiment of any of the foregoing lowpressure compressor, the low pressure compressor may include a lowpressure bleed comprising a bleed trailing edge, and a bleed trailingedge extending into the core flowpath beyond the outer diameter of thecore flowpath.

In a further non-limiting embodiment of any of the foregoing lowpressure compressor, the low pressure compressor may include amulti-stage compressor.

In a further non-limiting embodiment of any of the foregoing lowpressure compressor, the low pressure compressor may include an innerdiameter of the core flowpath that increases through the low pressurecompressor along a fluid flow direction.

In a further non-limiting embodiment of any of the foregoing lowpressure compressor, the low pressure compressor may include an outerdiameter slope angle that is operable to reduce a tip clearance of acompressor rotor, and thereby reduces flow separation.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a gas turbine engine.

FIG. 2 contextually illustrates an example core flowpath through a lowpressure compressor of the gas turbine engine of FIG. 1.

FIG. 3 contextually illustrates another example core flowpath through alow pressure compressor of the gas turbine engine of FIG. 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. Alternative engines mightinclude, for example, a three-spool design, an augmentor section, anddifferent arrangements of sections, among other systems or features. Thefan section 22 drives air along a bypass flowpath while the compressorsection 24 drives air along a core flowpath for compression andcommunication into the combustor section 26 then expansion through theturbine section 28. Although depicted as a turbofan gas turbine enginein the disclosed non-limiting embodiment, it should be understood thatthe concepts described herein are not limited to use with turbofans asthe teachings may be applied to other types of turbine engines.

The engine 20 generally includes a low speed spool 30 and a high speedspool 32 mounted for rotation about an engine central longitudinal axisA relative to an engine static structure 36 via several bearing systems38. It should be understood that various bearing systems 38 at variouslocations may alternatively or additionally be provided.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a low pressure compressor 44 and a low pressureturbine 46. The low pressure compressor 44 is the first compressor inthe core flowpath relative to the fluid flow through the core flowpath.The inner shaft 40 is connected to the fan 42 through a gearedarchitecture 48 to drive the fan 42 at a lower speed than the low speedspool 30. The high speed spool 32 includes an outer shaft 50 thatinterconnects a high pressure compressor 52 and high pressure turbine54. The high pressure compressor 52 is the compressor that connects thecompressor section to a combustor 56, and is the last illustratedcompressor 52 in the illustrated example of FIG. 1 relative to the coreflowpath. The combustor 56 is arranged between the high pressurecompressor 52 and the high pressure turbine 54. A mid-turbine frame 57of the engine static structure 36 is arranged generally between the highpressure turbine 54 and the low pressure turbine 46. The mid-turbineframe 57 further supports bearing systems 38 in the turbine section 28.The inner shaft 40 and the outer shaft 50 are concentric and rotate viabearing systems 38 about the engine central longitudinal axis A which iscollinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 57 includes airfoils 59 whichare in the core airflow path. The turbines 46, 54 rotationally drive therespective low speed spool 30 and high speed spool 32 in response to theexpansion.

The engine 20 in one example a high-bypass geared aircraft engine. In afurther example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than ten (10), the gearedarchitecture 48 is an epicyclic gear train, such as a planetary gearsystem or other gear system, with a gear reduction ratio of greater thanabout 2.25 and the low pressure turbine 46 has a pressure ratio that isgreater than about 5. In one disclosed embodiment, the engine 20 bypassratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout 5:1. Low pressure turbine 46 pressure ratio is pressure measuredprior to inlet of low pressure turbine 46 as related to the pressure atthe outlet of the low pressure turbine 46 prior to an exhaust nozzle. Itshould be understood, however, that the above parameters are onlyexemplary of one embodiment of a geared architecture engine and that thepresent invention is applicable to other gas turbine engines includingdirect drive turbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, withthe engine at its best fuel consumption—also known as “bucket cruiseThrust Specific Fuel Consumption (‘TSFCT’)”—is the industry standardparameter of lbm of fuel being burned divided by lbf of thrust theengine produces at that minimum point. “Fan pressure ratio” is thepressure ratio across the fan blade alone, without a Fan Exit Guide Vane(“FEGV”) system present. The low fan pressure ratio as disclosed hereinaccording to one non-limiting embodiment is less than about 1.6. “Lowcorrected fan tip speed” is the actual fan tip speed in ft/sec dividedby an industry standard temperature correction of [(Tambient degR)/518.7)̂0.5]. The “Low corrected fan tip speed” as disclosed hereinaccording to one non-limiting embodiment is less than about 1250ft/second.

With continued reference to FIG. 1, FIG. 2 is a sectional view of thegas turbine engine 20 of FIG. 1, contextually illustrating a lowpressure compressor 44 of the gas turbine engine 20. The core flowpath,identified herein as flowpath 120 or core flowpath 120, passes throughthe low pressure compressor 44 of the gas-turbine engine 20. The lowpressure compressor 44 includes multiple rotor 112/stator 114 pairs thatserve to drive air through the core flowpath 120. The rotors 112 areconnected to an inner shaft 40 via a compressor frame 142. Interspersedbetween each of the rotors 112 is a stator 114. The stators 114 areconnected to an outer frame 160. The illustrated low pressure compressor44 is referred to as a three stage compressor as three rotor 112/stator114 pairs are included. Additional stages can be added or removeddepending on design constraints via the addition or removal of rotor112/stator 114 pairs. A variable guide vane 130 is located at an inlet132 of the low pressure compressor 44. Alternately, one or more of thestators 114 could also be a variable vane 130. An exit guide vane 116 islocated at a fluid outlet 134 of the low pressure compressor 44. In theillustrated example of FIG. 2, the exit guide vane 116 also acts as astator 114 corresponding to the last rotor 112 of the low pressurecompressor 44. The core flowpath 120 has an inner diameter 154 and anouter diameter 152 measured with respect to the engine longitudinal axisA.

As the core flowpath 120 passes through the low pressure compressor 44,the outer diameter 152 slopes inward relative to the engine centrallongitudinal axis A toward the engine central longitudinal axis A. Theinner diameter 154 of the core flowpath 120 slopes outward relative tothe engine central longitudinal axis A away from the engine centrallongitudinal axis A resulting in an increasing inner diameter 154 as thecore flowpath 120 progresses along the direction of fluid flow. As aresult of the inward sloping outer diameter 152 and the increasing innerdiameter 154, the core flowpath 120 has a lower cross sectional area atthe fluid outlet 134 than at the fluid inlet 132, and air passingthrough the low pressure compressor 44 is compressed.

A steeper slope angle of the outer diameter 152, relative to the enginecentral longitudinal axis A, results in a greater average tip clearancebetween the rotor blade 112 and the engine case during flight. Theadditional tip clearance increases flow separation in the air flowingthrough the core flowpath 120. By way of example, undesirable amountsflow separation can occur when the outer diameter 152 exceeds 15 degreesrelative to the engine central longitudinal axis A.

Flow separation occurs when the air flow separates from the coreflowpath 120 walls. By ensuring that the outer diameter 152 includes asufficiently low slope angle, relative to the engine centrallongitudinal axis A, the flow separation resulting from the additionaltip clearance is eliminated, and the total amount of flow separation isminimized. In some example embodiments, a slope angle of the outerdiameter 152 is less than approximately 10 degrees relative to theengine central longitudinal axis A. In another example embodiment, theslope angle of the outer diameter 152 is approximately 6 degreesrelative to the engine central longitudinal axis A.

With continued reference to FIGS. 1 and 2, FIG. 3 illustrates an examplecore flowpath 120. In some example engine embodiments, air flow passingthrough the core flowpath 120 is not sufficiently stable. In order toincrease the stability of the fluid flow, and improve the pressure ratioof the low pressure compressor 44, one or more variable guide vanes 130are included in the flow path 120. In a three stage geared turbofancompressor 44, such as the one illustrated in FIG. 2, a single variableguide vane 130 can be utilized to sufficiently stabilize the air flow.However, alternate embodiments, such as those utilizing additionalcompressor stages, may require additional variable guide vanes 130. Insuch an embodiment, one or more of the stators 114 can be the additionalvariable guide vanes 130. In alternate examples, the air flow can besufficiently stable without the inclusion of a variable guide vane 130,and the variable guide vane 130 can be omitted.

In some example embodiments the exit guide vane 116 is incorporated intoa low pressure compressor outlet 134 section of the core flowpath 120the low pressure compressor 44, and to the high pressure compressor 52.The low pressure compressor outlet 134 section of the core flowpath 120is sloped inward (toward the engine central longitudinal axis A).Placing the exit guide vane 116 in the inward sloping low pressurecompressor outlet 134 section of the core flowpath 120 cants the exitguide vane 116 and provides space for a low pressure bleed 164. The lowpressure bleed 164 and allows for dirt, rain and ice to be removed fromthe compressor 44. The low pressure bleed 164 additionally improves thestability of the fluid flowing through the core flowpath 120. The lowpressure bleed 164 is positioned between the rotors 112 and the exitguide vane 116. In some example embodiments a bleed trailing edge 162 ofthe low pressure bleed 164 can extend inward toward the engine centrallongitudinal axis A, beyond the outer diameter 152 of the core flowpath120. In such an embodiment the outer diameter of the bleed trailing edge162 of the low pressure bleed 164 is smaller than the outer diameter152. Extending the bleed trailing edge 162 inwards allows the bleed 164to scoop out more of the dirt, rain, ice or other impurities that enterthe core flowpath 120.

Although a preferred embodiment of this invention has been disclosed, aworker of ordinary skill in this art would recognize that certainmodifications would come within the scope of this invention. For thatreason, the following claims should be studied to determine the truescope and content of this invention.

1. A turbine engine comprising: a compressor section having at least alow pressure compressor, and a core flowpath passing through said lowpressure compressor, said core flowpath having an inner diameter and anouter diameter, wherein said outer diameter has a slope angle of betweenapproximately 0 degrees and approximately 15 degrees relative to anengine central longitudinal axis; a combustor in fluid communicationwith the compressor section; and a turbine section in fluidcommunication with the combustor.
 2. The turbine engine of claim 1,further comprising a fan.
 3. The turbine engine of claim 2, wherein saidfan is connected to at least a low speed spool through a gearedarchitecture.
 4. The turbine engine of claim 1, wherein said slope angleis in the range of approximately 0 degrees to approximately 10 degreesrelative to said engine central longitudinal axis.
 5. The turbine engineof claim 4, wherein said slope angle is approximately 6 degrees relativeto said engine central longitudinal axis.
 6. The turbine engine of claim4, wherein said slope angle is in the range of approximately 5 degreesto 7 degrees, relative to said engine central longitudinal axis.
 7. Theturbine engine of claim 1, wherein said slope angle slopes toward saidengine central longitudinal axis along a fluid flow direction of saidcore flowpath.
 8. The turbine engine of claim 1, wherein said lowpressure compressor comprises at least one variable vane.
 9. The turbineengine of claim 1, wherein said low pressure compressor furthercomprises an exit guide vane, wherein said exit guide vane is located ina low pressure compressor outlet section of said core flowpath.
 10. Theturbine engine of claim 9, wherein said low pressure compressor furthercomprises a low pressure bleed located between a low pressure compressorrotor and said exit guide vane.
 11. The turbine engine of claim 10wherein said low pressure bleed further comprises a bleed trailing edge,and wherein said bleed trailing edge extends into said core flowpathbeyond said outer diameter of said core flowpath.
 12. The turbine engineof claim 1, wherein said low pressure compressor is a multi-stagecompressor.
 13. The turbine engine of claim 1, wherein said innerdiameter of said core flowpath increases through the low pressurecompressor along a fluid flow direction.
 14. The turbine engine of claim1, wherein said outer diameter slope angle is operable to reduce a tipclearance of a compressor rotor, and thereby reduce flow separation. 15.A low pressure compressor for a turbine engine comprising a coreflowpath, wherein said core flowpath has an inner diameter and an outerdiameter, and wherein said outer diameter has a slope angle of betweenapproximately 0 degrees and approximately 15 degrees relative to anengine central longitudinal axis about which said low pressurecompressor rotates.
 16. The low pressure compressor of claim 15, whereinsaid slope angle is between approximately 0 degrees and approximately 10degrees.
 17. The low pressure compressor of claim 16, wherein said slopeangle is approximately 6 degrees.
 18. The low pressure compressor ofclaim 15, further comprising at least one variable vane.
 19. The lowpressure compressor of claim 15, further comprising an outlet section ofsaid core flowpath, wherein said outlet section includes an exit guidevane.
 20. The low pressure compressor of claim 19, further comprising alow pressure bleed located between a low pressure compressor rotor andsaid exit guide vane.
 21. The low pressure compressor of claim 20,wherein said low pressure bleed comprises a bleed trailing edge, andwherein said bleed trailing edge extends into said core flowpath beyondsaid outer diameter of said core flowpath.
 22. The low pressurecompressor of claim 15, wherein said low pressure compressor is amulti-stage compressor.
 23. The low pressure compressor of claim 15,wherein said inner diameter of said core flowpath increases through thelow pressure compressor along a fluid flow direction.
 24. The lowpressure compressor of claim 15, wherein said outer diameter slope angleis operable to reduce a tip clearance of a compressor rotor, and therebyreduce flow separation.